International Patent Publication No. WO 93/23172 describes a conventional injection valve for direct injection of fuel into the combustion chamber of an internal combustion engine includes a valve body arranged in a housing and having a valve opening which is surrounded by a valve seat arranged on the spray side and through which there extends a valve needle carrying a closing head so that the closing head is in contact with the valve seat from the outside when the valve is closed.
When the valve needle moves out of its closed position against the force of a closing spring into the spraying direction in order to spray fuel, the closing head is lifted up from the valve seat, forming an annular spray opening between the closing head and the valve seat. The cross section of the spray opening is the narrowest cross section of the flow path, determining the flow rate, through the valve and is determined by the opening stroke of the valve needle.
The opening stroke of the valve needle is determined by an actuating device acting on the valve needle, or if there are alignment errors, by a spring sleeve attached to the valve needle coming to rest against a valve needle guide body. Due to manufacturing tolerances, it is therefore difficult to accurately set the desired cross section of the spray opening. Furthermore, in prolonged operation of the known an injection valve, changes may occur in the cross section of the spray opening, because the means for limiting the stroke, as well as the valve seat and the sealing surface connected thereto, are subject to wear.
U.S. Patent No. 5,307,997 describes another conventional injection valve which includes a valve seat body with a valve opening serving as a spray opening and a valve needle guide body with as guide bore for the valve needle. A sealing surface provided on the valve needle is connected to a valve seat surrounding the valve opening on the side facing away from the spray area. Upstream of the spray opening there is a frusto-conical swirl chamber bordered by a recess in the valve seat body and a projection on the valve needle guide body.
Fuel is supplied to the swirl chamber through bore holes in the valve needle guide body which form fuel channels. Each individual bore hole has a bore section with a reduced diameter toward the outlet end. These bore sections together form the narrowest cross section in the flow path through the injection valve required for fuel metering. Because of the swirl chamber downstream from the fuel channels, fuel with this conventional injection valve is sprayed in the form of a uniform, continuous frusto-conical layer of fuel.